Designed to shatter the sailing speed record, the Syroco speed craft challenges the paradigms of yacht design. We asked Romain and Hugo to explain the key concepts to us. 

First of all, how do you define a sailboat? 

Hugo: For most people, sailboats possess certain characteristics: one or more hulls, a rig made up of at least one mast which carries the sail(s) used for propulsion. 

Romain: Basically, in its purest concept, we can define a sailboat as a system (that is to say, a whole whose elements act in a coordinated fashion) which exploits the difference in speed between two fluids (air and water) to move in a terrestrial reference frame. 

How does a sailboat move forward, what are the limits? 

Romain: The element(s) moving in the air (sails, or what replaces them) generate aerodynamic forces directed forward (in the direction of travel) and leeward (drift). In water, the submerged elements (hulls, appendages) produce opposing hydrodynamic forces which prevent the boat from drifting, as well as a drag force. When sailing at constant speed, all the forces produced by the sailboat are balanced. On a conventional sailboat, these forces are not aligned and generate therefore a heeling moment that must be balanced by producing a righting moment. 

For this, we generally use the shapes of hulls and floats, the masses (keel, crew) or the lifting surfaces (foils on an Imoca). The maximum righting moment that can be generated is often what limits performance because it limits the intensity of the driving force that the sailboat can produce without capsizing and thus defines its power. In addition, producing this righting moment generally results in an increase in drag. 

Hugo: An important part of the architect's work actually consists in optimizing the power and efficiency of the boat, in order to maximize its performance: more driving force, less heeling force to compensate, less drag. But the laws of physics, which state that the drag is proportional to the square of the speed, make the combat unequal. 

How to go further, or rather go faster?

Hugo: What we have done at Syroco is to free ourselves from the general wisdom about what a sailboat is, and therefore from its limits. We put ourselves in an innovation design mode, for an exploratory phase. Helped by experts (not exclusively in the naval field), we said: there is no stupid idea, let's explore the universe of possible, starting from the basic concept. 

And by using in particular the work of our technical advisor Luc Armant (document in French), we decided to focus on the concept of the aile d’eau, derived from the “weightless yacht”.

What are the principles of the aile d’eau?

Hugo: As imagined by Luc, the aile d’eau directs the aerodynamic and hydrodynamic forces until they are perfectly opposed, thus eliminating the heeling moment. Consequently, the notion of righting moment disappears and it is no longer necessary to have recourse to the use of masses or specific appendages, which, as we have seen, generate additional drag. Power limits preventing the use of the full propulsive force generated by the wing are overcome.

Romain: Hence the term “weightless yacht”, which does not mean that the boat must not have weight, but that this weight is not necessary for the mechanical functioning of the system. In other words, it can be zero, or greater than zero - it's just a matter of properly sizing the elements. 

These components of the aile d’eau, what are they? 

Hugo: Basically, the aile d’eau is made up of two parts: 

• An aerial kite, which provides driving force (in the direction of movement), upward force and leeward force (downwind force).
• A hydrofoil, the sole purpose of which is to compensate for the vertical force (downwards) and to provide a side force (oriented to windward).

As perfection does not exist, the hydrofoil also induces drag... which we try to reduce as much as possible!

And the speed craft capsule, are we even talking about it? 

Romain: No! She might not exist, that wouldn't change a thing. 

Except that in real life, the vessel needs to be piloted. The aerial wing and the hydrofoil both have control systems. It is therefore necessary to embark one (or more) pilot(s), and/or servo systems, and/or radio control. It takes up space and weight. The sizing of the aerial wing ensures the ability for the machine to take off, and the aerodynamic profile of the capsule avoids adding more drag than necessary. 

Hugo: Of course, all this adds to the complexity. But that also makes the concept transposable beyond the speed record, since we can project towards vessels of different sizes, transporting passengers, goods... quickly, and only by the force of the wind. 

Romain Lanos is Principal Designer at Syroco. Holding a PhD. in applied physics and a DPEA in naval architecture, he worked with several offshore racing teams before joining Syroco to drive the speed record project. 

Hugo Roche holds a degree in naval architecture and marine engineering from the Ecole Centrale de Nantes. A specialist in hydrodynamics and numerical simulation, he is in charge of CFD and VPP studies at Syroco.